The purpose of this study is to characterize the epithelial cells in the normal, atrophic, regenerating, and neoplastic human gastric mucosae in respect to their fine structure, location in the gastric mucosa, enzyme cytochemistry, ability to synthesize DNA and undergo mitosis, and some metabolic and physiologic properties (such as their ability to synthesize certain physiologically active amines and peptides). This study is expected to produce significant information about the ontogenesis, maturation, and functioning of different types of epithelial cells in these normal, abnormal, and regenerating stomachs. Methods to maintain gastric mucosae in organ culture are expected to be developed, so as to be able to study the metabolism of the human gastric epithelia more effectively, and to be able to study the effects of various nutrients, gases, chemicals, and drugs upon the gastric mucosa, the epithelia in particular.